A biggest feature of a Universal Serial Bus (English full name: Universal Serial Bus, USB for short) Type-C interface is that the USB interface supports double-sided insertion, resolving a problem of “inaccurate insertion of USB”. Devices having USB Type-C interfaces may be classified, based on role configuration types supported by the devices, into a downstreaming facing port (English full name: Downstreaming Facing Port, DFP for short) device, an upstreaming facing port (English full name: Upstreaming Facing Port, UFP for short) device, and a dual role port (English full name: Dual Role Port, DRP for short) device. The USB Type-C specification stipulates that a DRP device may be configured as a DFP device or a UFP device based on a role of a peer end device during device connection establishment. Therefore, based on the USB Type-C specification, when two DRP devices having USB Type-C interfaces are connected to each other, whether each of the devices is configured as a DFP device or a UFP device is random. However, the randomness may lead to some cases against common sense. For example, a user wants to charge, by using a tablet computer at a relatively high battery level, a mobile phone at a relatively low battery level. However, because the two devices are both DRP devices, random role allocation leads to an “awkward situation” in which the mobile phone at a relatively low battery level charges the tablet computer at a relatively high battery level.
To avoid such an inappropriate scenario in which “a mobile phone charges a notebook computer”, the USB Type-C specification defines two extended roles of the DRP: Try.SNK (trying to be a UFP device) and Try.SRC (trying to be a DFP device). It is expected to avoid the foregoing “awkward situation” by configuring computers and notebook computers as Try.SRC roles and configuring mobile phones and tablet computers as Try.SNK roles. However, when a tablet computer is connected to a mobile phone, or mobile phones are connected to each other, because they are both Try.SNK devices, there is still an awkward situation in which “a device at a relatively low battery level charges a device at a relatively high battery level”.